Cameron mentioned mineral wool. Fine Homebuilding #254 (Sept, 2015) had an article on mineral wool last year. Costly, but you don't need that much for a trailer. Better than fiberglass. Check it out. You may have to pay to see the article or go to the library.

I have spent the entire afternoons reading this thread. Having belonged to several different forums on different subject matters, I can only say that I have never read a thread more confusing.

You have to seal it completely, but let it breathe and drain moisture?? The various “sides” in this discussion are all searching for a perfect solution that does not seem to exist.

Although no mention of it was made on this thread, I just ran across an AS restoration that used a soy-based spray foam!! I cannot imagine anything more ridiculous. I have a Toyota Tundra in which they used soy-based tubing. The mice come from miles around to feast on it.

To use arguments against spray foams that were applied back in the 70’s is pointless. Everyone should know how much these products have changed since then. Also, to argue that they would turn to powder would assume they were applied in a “drill and fill” method and the foam was adhering to both skin surfaces.

As far as I can glean, the only valid argument against spray foam is how they would complicate future body repairs. As far as wiring changes, the conduit solution mitigates that.

Moisture retention below damaging the chassis/frame could be prevented by an application of POR-15 (which should be done anyway).

I still have not made up my mind on drilling holes through the sill and C-channel to let moisture drain. Seems like an invitation to insect intrusion?

The application of some self-adhering foam tape to the ribs before re-installing the interior skins sounds like a great ideas. Does anyone who followed through with this have any feedback yet?

I have just begun to remove the interior skins on my ‘76 31’ Sovereign, so I am trying to decide which method to use.

The application of some self-adhering foam tape to the ribs before re-installing the interior skins sounds like a great ideas. Does anyone who followed through with this have any feedback yet?

We applied sill seal (the pink stuff traditionally used on top of foundation stem walls between the concrete and wood wall sills) on our ribs, underneath the inner skin. Used 3M double-sided tape. During the intense heat and direct sun we had this summer those ribs with the sill seal were definitely cooler than those that were still open to the interior.

The application of some self-adhering foam tape to the ribs before re-installing the interior skins sounds like a great ideas. Does anyone who followed through with this have any feedback yet?

I did this. I'm happy with the performance of my insulation. Parked in direct sunlight with an exhaust fan running, inside temps are approximately the same as sitting under a shady tree. A thermal break on the ribs seems to help a lot, but I have only my subjective experience to back that up.

HofArc uses spray foam. Timeless Travel uses Polyisocyanurate panels. Those are two of the "best" high end resto/renovation companies around, so I'd say those are probably the two best options. Which one you use is up to you after weighing all the reasons for either.

As far as moisture goes... I don't think anyone with a lot of real world experience has weighed in on the matter (a lot of people have theorized). Airstreams come with weep holes from the factory, and it seems to me that if your walls have cavities (open space), allowing for "breathing" and draining is a good idea. However, if you're going with spray foam, it seems less necessary, as theoretically everything will be sealed.

I went with Polyisocyanurate because it was so much easier to do different sections at a time over a longer time period (spray foam has to be done all at once or it gets expensive and messy).

I used 3M sill plate foam on the ribs (what is used between foundation and frame on a building), and it makes a HUGE difference in the sun.

We looked at spray foam and were in the process of getting everything ready but have now backed out of the idea.

I would reconsider spray foam if it wasn't our first Airstream reno. Spray foam seems very unforgiving on the "oops" and "oh crap" moments that we will have. When you have renovated hundreds of trailers, you rarely make mistakes but that is NOT us! Lol

We looked at spray foam and were in the process of getting everything ready but have now backed out of the idea.

I would reconsider spray foam if it wasn't our first Airstream reno. Spray foam seems very unforgiving on the "oops" and "oh crap" moments that we will have. When you have renovated hundreds of trailers, you rarely make mistakes but that is NOT us! Lol

To me it seems like a lot of trouble and expense for a limited return and I kinda like that fiberglass wont burn even if a person holds a torch to it.

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The fact that I am opinionated does not presuppose that I am wrong......

Sorry if this is a bit off topic, but I am curious about how you reinstall the inner skin after putting insulation on the ribs. Do the original rivet holes still match up, or do you have to fudge things?

Sorry if this is a bit off topic, but I am curious about how you reinstall the inner skin after putting insulation on the ribs. Do the original rivet holes still match up, or do you have to fudge things?

The radius will decrease slightly, the holes will not align as they had previously. Some holes in the skin will need to be elongated.

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The fact that I am opinionated does not presuppose that I am wrong......

It is true you want to seal perfectly to prevent air intrusion while allowing the trailer to breathe and water to drain. Doing that with a house is hard enough, adapting a trailer to that standard is very, very difficult. But it can be done with spray foam. I would seal all places where air can flow 9like seams) with tape made for insulating, then spray. There are a variety of spray foams available and researching on sites about home building will help. I have read many articles about foam spray and since I was not going to do it in my house, pretty much forgot what I read. It is impossible to make a perfect seal (air circulation through cracks, holes, etc., seriously degrades any insulation), but you try hard to get perfect. New houses that are well sealed, use heat exchanger ventilation systems to bring fresh air in, warmed (or cooled in summer) by the exchanger. That is pretty much overkill in a trailer plus it needs 120 v. Better to open a vent to clear the air from time to time.

Trying to airseal fiberglass insulation is very difficult. Professionals often get it wrong. It may well have an actual R value half of the rating. Bouncing down the road and leaks also degrade fiberglass or cause it to sink down the wall. To reduce thermal bridging you can put something that transmits less heat between the inner and outer skins where they are attached to the ribs. Those are available from the construction industry, but I suppose a thin piece of dense foam would help.

We sold our Airstream and bought a Northwood Mfg. product with foam board vacuum pressed into the walls. I think they use it in the ceiling and around the undercarriage and tanks. The difference in heat transfer (actually lack of it) is dramatically different. We would travel for several hours with the Airsteam and stop for lunch in a super heated trailer in summer. We also have thermal pane windows and have had no problems with them. With our new trailer, it is hot, but not terribly so. We save money on propane (for heat, fridge) and don't have to run the A/C nearly as much.

Airstream has a habit of trying things not having thought it all through, failing and never doing it again. That is the mark of a company which has too many old timers who can't learn. Thus the bad experience back in the 1970's with thermal pane windows and foam insulation means, no matter what has changed, Airstream can't change until everyone dies.

For 40% of the cost, our new trailer is much better insulated, has some real improvements in other ways, doesn't tow as well, but otherwise is easier to use. We are not cool anymore, but we are a lot more comfortable. It was sad to see our Airstream being towed away, but we moved on. Research foam spray and you'll be confused, but it is the way to go.

To folks who have applied closed-cell foam: how much do you need to be concerned with rivet sealing before/after installing the insulation?

I'm thinking about how to approach a full reno for a unit that will become a stationary tiny vacation house, used in the summer. Ideally, I'd like to repair any obvious bad rivets before applying the foam. But if I missed one, or one went bad, wouldn't the foam contain any water intrusion? I would think that people who have used foam have nearly no water gathering in their U channel and/or damaging their floor at the perimeter. Practically, this means that I wouldn't need to spend the time going over every rivet with a suction cup and doing a lot of replacement. Rivets at the ribs and windows, however, would need the attention.

As I think about using foam, I'd likely apply it down to about 6" above the floor, allowing access to the flooring bolts, and offering a place to run/access wires, if needed, after sealing up the rest of the walls (where the other wires would be inaccessible).

Every form of insulation has negatives to it. First I would seal any holes, seams or other places that water can come in on the interior (and exterior where it would work). There are a number of insulating paper, plastic and other products used to seal around windows and doors and other holes in houses. It is self sticking. Use a lot, and then spray. Once you spray, obviously things get hard to get to. If you can leave some space between the foam and the inner wall, that's where to run wires and plumbing. Maybe you can build channels in the foam out of tubing. Vinyl tubing is available anywhere and if you can a find a large enough diameter piece, hopefully you can thread wires and flexible pipe through it.

You have to think about air sealing, something that is done at the exterior under the siding or inside, usually under the drywall, or even in between in complex walls. Insulation is not too useful if air can get in through holes you may not even see, but air moves through all buildings. Some are better sealed and thus better insulated. You don't have a lot of room between the walls in an Airstream, but you can certainly do a better job than using the fiberglass batts Airstream refuses to give up.

Will water get through sealant and self sticking sealers? Depends on how anal retentive you are, but I would hope you can reduce it to a little vapor and that will be it. Cars and trucks can sealed, why can't trailers? I look at the trailer as more like a house, but cars use a lot of rubber and windows and door rubber seals could be renewed. Various boxes with access from both sides—furnace, water heater, fridge, need to be looked it inside and out.

Look for places where there is an easy way to pass cold and hot temperatures. Metal is really good at this, but wood does it too. Place a thin piece of a noninsulating barrier between the skins and the frame.

You can put some weep holes at the bottom to let water out, but if you do the exterior sealing well, the water will come from condensation in the trailer.